Mybatis动态SQL

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转载自 Mybatis动态SQL

1. Mybatis if

如果Product的字段比较多的话，为了应付各个字段的查询，那么就需要写多条sql语句，这样就变得难以维护。

这个时候，就可以使用Mybatis 动态SQL里的if标签

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<select id="listProduct" resultType="Product">
	select * from product_
	<if test="name!=null">
		where name like concat('%',#{name},'%')
	</if>                         
</select>

如果没有传参数name,那么就查询所有，如果有name参数，那么就进行模糊查询。

这样只需要定义一条sql语句即可应付多种情况了，在测试的时候，也只需要调用这么一条sql语句listProduct 即可。

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
        <select id="listProduct" resultType="Product">
            select * from product_
            <if test="name!=null">
                where name like concat('%',#{name},'%')
            </if>        
        </select>
         
    </mapper>

TestMybatis.java

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package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
  
        System.out.println("查询所有的");
        List<Product> ps = session.selectList("listProduct");
        for (Product p : ps) {
            System.out.println(p);
        }
         
        System.out.println("模糊查询");
        Map<String,Object> params = new HashMap<>();
        params.put("name","a");
        List<Product> ps2 = session.selectList("listProduct",params);
        for (Product p : ps2) {
            System.out.println(p);
        }      
         
        session.commit();
        session.close();
  
    }
}

2. Mybatis where

1.1 多条件的矛盾

如果要进行多条件判断，就会写成这样：

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<select id="listProduct" resultType="Product">
	select * from product_
	<if test="name!=null">
		where name like concat('%',#{name},'%')
	</if>		 	
	<if test="price!=0">
		and price > #{price}
	</if>		 	
</select>

这么写的问题是：当没有name参数，却有price参数的时候，执行的sql语句就会是：

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select * from product_ and price > 10.

这样执行就会报错

多条件的矛盾

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
    <select id="listProduct" resultType="Product">
        select * from product_
        <if test="name!=null">
            where name like concat('%',#{name},'%')
        </if>        
        <if test="price!=0">
            and price > #{price}
        </if>        
    </select>
         
    </mapper>

TestMybatis.java

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
    <select id="listProduct" resultType="Product">
        select * from product_
        <if test="name!=null">
            where name like concat('%',#{name},'%')
        </if>        
        <if test="price!=0">
            and price > #{price}
        </if>        
    </select>
         
    </mapper>

1.2 where标签

这个问题可以通过标签来解决，如代码所示

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<select id="listProduct" resultType="Product">
	select * from product_
	<where>
		<if test="name!=null">
			and name like concat('%',#{name},'%')
		</if>		 	
		<if test="price!=null and price!=0">
			and price > #{price}
		</if>	
	</where>	 	
</select>

标签会进行自动判断

如果任何条件都不成立，那么就在sql语句里就不会出现where关键字

如果有任何条件成立，会自动去掉多出来的 and 或者 or。

所以在测试代码里

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Map<String,Object> params = new HashMap<>(); 
//params.put("name","a");
params.put("price","10");

这个参数map，无论是否提供值否都可以正常执行

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
    <select id="listProduct" resultType="Product">
        select * from product_
        <where>
            <if test="name!=null">
                and name like concat('%',#{name},'%')
            </if>        
            <if test="price!=null and price!=0">
                and price > #{price}
            </if>
        </where>     
    </select>
         
    </mapper>

TestMybatis.java

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package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
  
        System.out.println("多条件查询");
        Map<String,Object> params = new HashMap<>();
//        params.put("name","a");
        params.put("price","10");
        List<Product> ps2 = session.selectList("listProduct",params);
        for (Product p : ps2) {
            System.out.println(p);
        }      
         
        session.commit();
        session.close();
  
    }
}

1.3 set标签

与where标签类似的，在update语句里也会碰到多个字段相关的问题。 在这种情况下，就可以使用set标签：

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与where标签类似的，在update语句里也会碰到多个字段相关的问题。 在这种情况下，就可以使用set标签：

其效果与where标签类似，有数据的时候才进行设置。

set标签

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
    <select id="listProduct" resultType="Product">
        select * from product_
        <where>
            <if test="name!=null">
                and name like concat('%',#{name},'%')
            </if>        
            <if test="price!=null and price!=0">
                and price > #{price}
            </if>
        </where>     
    </select>
     
    <update id="updateProduct" parameterType="Product" >
        update product_
        <set>
            <if test="name != null">name=#{name},</if>
            <if test="price != null">price=#{price}</if>
              
        </set>
         
         where id=#{id}   
    </update>
         
    </mapper>

TestMybatis.java

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package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
 
        Product p = new Product();
        p.setId(6);
        p.setName("product zz");
        p.setPrice(99.99f);
        session.update("updateProduct",p);
         
        listAll(session);
 
        session.commit();
        session.close();
  
    }
 
    private static void listAll(SqlSession session) {
        Map<String,Object> params = new HashMap<>();
//        params.put("name","a");
//        params.put("price","10");
        List<Product> ps2 = session.selectList("listProduct",params);
        for (Product p : ps2) {
            System.out.println(p);
        }
    }
}

1.4 trim标签

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<trim prefix="WHERE" prefixOverrides="AND |OR ">
  ... 
</trim>

来替换

set标签就可以用

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<trim prefix="SET" suffixOverrides=",">
  ...
</trim>

来替换
运行set标签中的代码，其效果是一样的。

3. choose

3.1 if else

Mybatis里面没有else标签，但是可以使用when otherwise标签来达到这样的效果。

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<select id="listProduct" resultType="Product">
	  SELECT * FROM product_ 
	  <where>
	  	<choose>
		  <when test="name != null">
		    and name like concat('%',#{name},'%')
		  </when>			  
		  <when test="price !=null and price != 0">
		    and price > #{price}
		  </when>			  		
	  	  <otherwise>
	  	  	and id >1
	  	  </otherwise>
	  	</choose>
	  </where>
</select>

起作用是： 提供了任何条件，就进行条件查询，否则就使用id>1这个条件。

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
        <select id="listProduct" resultType="Product">
              SELECT * FROM product_
              <where>
                <choose>
                  <when test="name != null">
                    and name like concat('%',#{name},'%')
                  </when>          
                  <when test="price !=null and price != 0">
                    and price > #{price}
                  </when>                
                  <otherwise>
                    and id >1
                  </otherwise>
                </choose>
              </where>
        </select>
    </mapper>

ThesMybatis.java

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package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
 
        Map<String,Object> params = new HashMap<>();
//      params.put("name","a");
//      params.put("price","10");
      List<Product> ps = session.selectList("listProduct",params);
      for (Product p : ps) {
          System.out.println(p);
      }
 
        session.commit();
        session.close();
  
    }
 
    private static void listAll(SqlSession session) {
 
    }
}

4. foreach标签

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SELECT * FROM product_ 
	WHERE ID in
		<foreach item="item" index="index" collection="list"
   			open="(" separator="," close=")">
     		             #{item}
		</foreach>

foreach标签通常用于in 这样的语法里，参考 Oracle的in语法 。
如例，如图查询出id等于1,3,5的数据出来。

foreach标签

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
    <select id="listProduct" resultType="Product">
          SELECT * FROM product_
            WHERE ID in
                <foreach item="item" index="index" collection="list"
                    open="(" separator="," close=")">
                    #{item}
                </foreach>
    </select>
    </mapper>

TestMybatis.java

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package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
 
        List<Integer> ids = new ArrayList();
        ids.add(1);
        ids.add(3);
        ids.add(5);
         
      List<Product> ps = session.selectList("listProduct",ids);
      for (Product p : ps) {
          System.out.println(p);
      }
 
        session.commit();
        session.close();
  
    }

5. bind标签

bind标签就像是再做一次字符串拼接，方便后续使用
如本例，在模糊查询的基础上，把模糊查询改为bind标签。

Product.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.how2java.pojo">
        <!-- 本来的模糊查询方式 -->
<!--         <select id="listProduct" resultType="Product"> -->
<!--             select * from   product_  where name like concat('%',#{0},'%') -->
<!--         </select> -->
             
        <select id="listProduct" resultType="Product">
        	<!-- bind标签作用是 ,创建一个变量并将其绑定到上下文.-->
            <bind name="likename" value="'%' + name + '%'" />
            select * from   product_  where name like #{likename}
        </select>
         
    </mapper>

TestMybatis.java

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package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
 
        Map<String, String> params =new HashMap();
        params.put("name", "product");
         
          List<Product> ps = session.selectList("listProduct",params);
          for (Product p : ps) {
              System.out.println(p);
          }
 
        session.commit();
        session.close();
  
    }
 
}
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